Check engine light reset?

What I would do: Plug an OBD II reader into the socket under the dash. Use it to read the codes and record them on paper. Replace/repair the cause of the check engine light. Use the reader to reset the codes and light. This assumes that the Subaru is using the standard OBD II interface but AFAIK it has been mandatory since 1996.

Take a look at this:

I bought an ODBII reader from Wal Mart for $100. Haven't regretted it. They had a cheaper one that didn't have a text display.

Or you can take it to Auto Zone on a day they're not busy, and they'll read the code for ya. Not sure though if they'll reset one for you though.

-- Todd H.

I've read that in a few places, the local emissions testing board doesn't like the autoparts retailers resetting the CEL (though the testing computer should reject the car for not ready status - w'ever).

You could try carefully removing your NEG. battery cable, stepping on the brake pedal - waiting 15 minutes or so, then reconnecting (if it matters to you, you may need to write down your radio station presets as they might be lost.)

what seems to be wrong with your car?

I've read that in a few places, the local emissions testing board doesn't like the autoparts retailers resetting the CEL (though the testing computer should reject the car for not ready status - w'ever).

You could try carefully removing your NEG. battery cable, stepping on the brake pedal - waiting 15 minutes or so, then reconnecting (if it matters to you, you may need to write down your radio station presets as they might be lost.) Keep in mind, the car will revert to the factory 'map' and if the system has made adjustments for changes in the sensors - the car may run poorly for a few drive cycles.

what seems to be wrong with your car?

If the problem that set a code and caused the light to turn on is no longer detected over a few driving cycles, the light will go off on its own and you don't have to do anything. Although it's possible to clear the code and turn off the light by disconnecting/reconnecting the battery, this is not a good idea for a few reasons some of which have been mentioned here-

- Disconnecting the battery will erase the code from memory so it cannot be retrieved later. This hinders troubleshooting of the problem. Best to leave the battery alone, and get the code read out with an OBDII reader to find out what may be wrong. After the code is read, it can be cleared electronically with the reader/scanner or just left alone.

- Pulling the battery will also erase your radio presets and you will have to re-enter them.

- A full power reset will also clear the learned data in the ECU and the car may not run the same for a while until it re-learns.

If you don't have access to a scanner, you can go to an Autozone (as long as you are in the US in any state other than CA) and they will scan it for free. Just be sure to get the actual code from them (it will be in Pxxxx format), you can then do an online search to find more information about that particular code and what causes it.

If you are in a state that does OBDII inspections, do not go for an inspection immediately following a reset or code-clearing. Even when the codes are cleared electronically with no battery disconnect, the OBD readiness monitors will be reset and have to complete their cycles from the beginning which can take several days and/or a few hundred miles of driving. Therefore you'll fail inspection if you go during this period before the monitors are complete. You'll also fail if you go for inspection while the light is on and there are active codes.

Thanks, took your advice and bought one from Amazon. Not quite as cheap, but with two cars it is worth it.

JJ

I have had luck having my autozone reset my light. Advance also does free OBDII readings.

Although you said you've already bought your meter, I would've suggest that you buy an OBDII-USB cable and plug it into your laptop with appropriate free software, it's the cheapest way.

Yousuf Khan

Thanks but I don't own a laptop. Shocking I know!

Just as an update to my earlier post about autozone doing free readings. I had my check engine light come on the other night on the way home from work. I was already going to advance to buy plug wires for my other subie, so I asked them if they'd read codes. They said they'd just give me the checker if I left my license. I don't know if it was that they were busy(they had two people not doing anything with customers) or if that is their normal policy, but I got to do all the button pushing. I cleared the P0420 code and returned the reader.

Oddly, when I restarted the car, it dipped down to under 500 RPM, then revved up to 1200 or so a few times before settling into a smooth idle. It hasn't done it since. Is this normal? Is it because I cleared a code without fixing the problem and the ECU had somehow been compensating for that problem, but then wasn't? Or is it because the ECU had learned an engine map and now was starting from a base map? (I've read in either car and Driver or Road and Track that subarus can lose 10 to 15 horses on the dyno immediately after clearing the ECU since they have addaptive mapping.)

I'd say you're right on both counts. Hard to know HOW MUCH the oxygen sensor/w'ever had drifted from 'ideal' so, even without the code, clearing the ECU and forcing it to return to the default map may have given you some odd running conditions for a few drive cycles anyway.

Carl

I believe your later conjecture is the right one here. And yeah, when I reset my p0420 I see similar results so I'll call it normal.

-- Todd H.